A. Field of the Invention
This invention relates to a method for improving the efficiency of a conveyor belt in transporting particulate solids, particularly at temperatures below freezing, i.e., 0.degree. C.
B. Description of the Prior Art
In transporting particulate solids such as coal, ores, gravel, and other substantially water insoluble particulates on conveyor belts, a serious problem is that in freezing temperatures, a substantial amount of slippage occurs between the particulate and the belt surface as ice accumulates on the belt surface, on the surfaces of the particles, or on both. The problem is particularly severe where at least a portion of the belt is outdoors and thus exposed to moisture from sleet and snow as well as to moisture from condensation and that which may be on the surface of the particulate. Obviously, such slippage results in decreased material handling efficiency, wasted energy in driving the belt under inefficient conditions, and in severe conditions can result in a temporary plant shut down, e.g., if coal cannot be delivered to its point of use at a sufficient rate to maintain a furnace or boiler at proper operating conditions.
Various techniques have been tried to alleviate the slippage problem, such as spraying the belt with ethylene glycol. Conventional antifreeze compositions, however, have not been regarded as a completely acceptable solution to the problem, since benefits seem to be realized only at mild freezing temperatures, e.g., temperatures above about 20.degree. F. (-6.degree. C.). Consequently, smudge pots or heaters are often placed near a belt to heat the belt. However, in the event the conveyor must be stopped for a brief period, the heat sources near the belt are a serious hazard since not infrequently, the belts are burned by the heat source.
Various deicing or freeze depressant compositions have been taught, particularly for use on aircraft. Representative of this art are the following patents:
Korman, U.S. Pat. No. 2,101,472, which teaches a gel containing gelatine to which is added as an antifreeze substance, glycerol and/or a glycol; West et al., U.S. Pat. No. 2,373,727, which teaches a composition such as in Korman, but also including a hydrocarbon to provide an emulsion; Fain et al., U.S. Pat. No. 2,716,068, which teaches a composition of a glycol, at least one of potassium thiocyanate, potassium acetate, urea, or certain inorganic salts, and optionally sodium nitrite; British 1,055,453 which teaches a deicing composition of at least one water soluble monohydric alcohol, at least one water soluble polyhydric alcohol, and formamide or a formamide derivative; and Dawtrey et al., U.S. Pat. No. 3,350,314, which teaches a foamable composition of water, an alkylene polyol, and a long chain aliphatic tertiary amine.
Ordelt et al., U.S. Pat. No. 3,362,910, teaches an automotive antifreeze composition.
Scott, Jr., et al., U.S. Pat. Nos. 3,624,243 and 3,630,913, each relate to chemical deicers containing corrosion inhibitors making them specially suited for use on airport runways.
Shapiro, U.S. Pat. No. 2,454,886 relates to the prevention of mist and frost on glass and similar sheet material.
In a commonly assigned application entitled "Method for Reducing the Strength of Ice" by Christ F. Parks and Kenneth H. Nimerick, Ser. No. 855,528 filed Nov. 28, 1977, now U.S. Pat. No. 4,117,214 issued Sept. 26, 1978 which is a continuation-in-part of Ser. No. 380,778 filed July 19, 1973, now abandoned it is disclosed a multicomponent composition similar to that employed herein reduces the strength of ice, and that a mass of particulate solids treated with the composition may be easily broken apart even after the mass is exposed to temperatures sufficient to permit ice to form because the ice which forms is of substantially reduced compressive strength.
There is no suggestion, however, that any of these formulations could be effectively used on conveyor belts.
In an invention on which a patent application is being filed concurrently herewith, now U.S. Pat. No. 4,163,079 issued July 31, 1979, Frank J. Beafore has discovered that the composition employed in the invention of Parks et al. is effective in meeting the problem of particulate slippage on belts at temperatures of less than 0.degree. C. The present invention is a further refinement of the invention of Beafore.
Finally, dimethyl polysiloxanes have been used as release agents for conveyor belts. See, for example, Dow Corning Corporation Bulletin 22-082 (March, 1972) "Information About Release Agents: Dow Corning HV-490 Emulsion". However, so far as is known there has been no suggestion to use the dimethyl polysiloxanes in the manner of the present invention.